111 EXPRESSION OF PHOSPHOLIPASE A2 ISOFORMS IN EQUINE ENDOMETRIUM DURING THE ESTROUS CYCLE AND EARLY PREGNANCY

Abstract

Phospholipase A2 (PLA2) is involved in the synthesis of prostaglandins (PG) as it releases arachidonic acid from the membrane phospholipids to be a precursor for cyclooxygenase enzymes. Therefore, it is critically important during luteolysis and at the time of maternal recognition of pregnancy. The embryo must attenuate endometrial PGF2α production, whereas PGE2 is considered to be luteoprotective. Furthermore, implantation also requires the action of PGs. A balance should be maintained in PG synthesis in the endometrium. The objective of this study was to evaluate the expression of isoforms of PLA2 (cytosolic [cPLA2], secretory [PLA2], and calcium independent [iPLA2]) in equine endometrium during the oestrous cycle and early pregnancy. Biopsies were obtained from mares on the day of ovulation (d0, n = 4), late diestrus (LD, n = 4, high progesterone [P4]), and after luteolysis in the beginning of oestrus phase (AL, n = 4, <1 ng mL–1 P4) of the cycle. Biopsies were also taken on days 14 (P14, n = 4), 18 (P18, n = 4), and 22 (P22; n = 4) of pregnancy. Relative mRNA expression levels of genes were quantified using real-time quantitative RT-qPCR. Data were analysed using one-way ANOVA and l.s.d. test. Compared with the day of oestrus (d0), steady-state levels of cPLA2 and sPLA2 were down-regulated at LD, where P4 was high, and expression of both were up-regulated again at AL. In contrast, iPLA2 expression was higher at LD and then decreased again at AL. Pregnancy decreased expression of cPLA2 and sPLA2 mRNA at P14 and P18 compared with their respective cycle days. Late diestrus elevation in the expression of iPLA2 was suppressed by pregnancy at P14; however, it was up-regulated later in pregnancy at P22. The results suggest that expression of cPLA2 and sPLA2 is negatively correlated with circulating progesterone concentrations. Pregnancy further inhibits their expression in the equine endometrium. However, iPLA2 expression seems to be positively correlated by progesterone presence and its expression increased as equine pregnancy advanced. This project was partially funded by TUBITAK 107O035 and SUBAP to AG.